1. Field of the Invention
The present invention relates to a drilling head for a self-drilling anchor and, in particular, for an injection anchor.
2. Description of the Prior Art
As is known in the prior art, drilling heads and other drilling apparatus have a distal end which contacts the material to be drilled, and a proximal end which is attached to a drive mechanism, with the drive mechanism driving the drilling head or apparatus into the material. In injection self-drilling anchors having a diameter of about 50 mm and which are mostly used in the mining industry, there is provided, on the distal end of a thin-walled anchor tube, which has an outer shaped profile and is glued to a bore wall with a reaction hard mortar, a radially projecting drilling head that is mostly equipped with hard metal cutter means. The necessary service life of the drilling head is determined by the length of the injection self drilling anchor and by the properties of a constructional component in which the anchor is to be secured. Because one-time, usable injection self-drilling anchors are needed in large quantities, their effective and material-saving manufacturing is of great importance. It is also important to minimize the annular gap between the anchor tube and a bore wall because with a thinner gap, gluing of the anchor tube with the bore wall is improved. This also results in minimization to the need in the reaction hard mortar.
German document DE 44 30 784 discloses an injection self-drilling anchor of the type described above in which the cutters on the distal end, with the cutters composed of a hard material, are directly welded to a thin-walled anchor tube having a shaped outer profile. According to German Patent DE 37 24 165 C2, an injection self-drilling anchor is provided at its distal end with a plate-shaped drilling head that is bluntly secured on a relatively thick anchor tube with a shaped outer profile. According to German Utility Model DE 20021835 U1, an injection self-drilling anchor is provided at its distal end with a drilling head having cutters of a hard material and which is bluntly secured on a relatively thick anchor tube having a shaped outer profile. A direct fixing of cutters or drilling head, using a foreign material, is technologically disadvantageous because it is not modular. In addition, use of an additional brazing or welding process, with large quantities of anchors, is noticeably more expensive.
U.S. Pat. No. 4,540,200 discloses a rock anchor a drilling head of which that is provided with hard material cutters, is secured with its inner cone part on a smooth thick-walled drill shaft. With an inner cone part radially projecting beyond the drill shaft diameter and with cutters that necessarily radially project beyond the cone part, a wider annular gap is formed between the drill shaft and a bore wall and which is unacceptable in the injection self-drilling anchors. A thin-walled drilling rod, which is guided in the inner cone part, can fail because of buckling.
U.S. Pat. No. 3,144,912 discloses a wall drill having a diameter of about 10 mm and a one-piece cross-shaped drilling head that is forcelockingly secured with a tubular drill shaft by its four outer edges extending conically outwardly. This filigree embodiment suitable for manual drilling is not suitable for substantially wider self-drilling anchors because the anchor tube undergoes a non-circular deformation due to a circumferentially pointed fixation of the drilling head, when the drilling head is pressed in the anchor tube.
Accordingly, an object of the present invention is a drilling head for a self-drilling anchor having a diameter in a range from 30 mm to 60 mm.